1. Technical Field
The present invention relates to an image display apparatus and an image display method.
2. Related Art
In a projection-type image display apparatus of such as a projector, in the case where the image display apparatus includes light modulation devices such as liquid crystal light valves, the resolution of an image projected on a screen is typically equal to the resolution of the light modulation devices (the number of horizontal pixels, the number of vertical pixels). In the following explanation, “resolution of image projected on screen” will be referred to as “display resolution”. Here, as a method of improving the display resolution without changing the resolution of the light modulation devices, there is a method of increasing the number of light modulation devices and performing projection while shifting the positions of the images of the respective pixels formed by the respective light modulation devices on the screen. However, according to the method, it is necessary to increase the number of light modulation devices, and there is a problem that significant increase in costs is caused.
As a method of solving the problem, a method of shifting the positions of the images of the respective pixels not spatially but along the temporal axis has been proposed (for example, see Patent Documents 1, 2 (JP-A-11-298829, JP-A-2005-91519)). According to the method, it is unnecessary to increase the number of light modulation devices. In Patent Document 1, as a specific example, a configuration in which a parallel plate is inserted between the light modulation devices and a projection lens at a tilt relative to the normal line of the optical axis, the optical axis is shifted with respect to each field by changing the tilt angle of the parallel plate, and the positions of the pixels are temporally shifted has been proposed. As another specific example, a configuration in which a rotating plate having two regions different in refractive index or amount of refraction is obliquely inserted between the light modulation devices and the projection lens, the optical axis is shifted by rotating the rotating plate, and the positions of the images of the pixels are temporally shifted has been proposed.
Note that, in the following explanation, temporal (temporal axis) shift of the positions of the images of the respective pixels on a projection surface may be referred to as “temporal axis pixel shift” for convenience.
However, as in Patent Documents 1, 2, the image display apparatus in related art of employing the temporal axis pixel shift technology constantly performs display while shifting the positions of the images of the respective pixels along the temporal axis regardless of contents of externally input images. The temporal axis pixel shift technology is to improve the display resolution by displaying images for one frame in the shifted positions using two frames for pixel shift, for example. In other words, the temporal axis pixel shift technology is a technology of improving the spatial resolution at the expense of the temporal resolution. Therefore, the technology is suitable for still images having no temporal frequency components, but not suitable for moving images having temporal frequency components. For example, deterioration of image quality such that images moving at a high speed blur may be caused.
Further, in the apparatus of Patent Document 2, as means for reducing blur of the images, a technology of inserting a frame for black representation between plural frames for image display has been disclosed. However, in the case of using the technology, there is a problem that the brightness of display is deteriorated by the insertion of the black representation.